A wide variety of hydrocarbon conversion processes encountered in the petroleum refining industry are catalytic in nature and many of these processes use crystalline aluminosilicate zeolites as catalysts. Illustrative of such processes include, for example, dewaxing, hydrodewaxing, cracking, hydrocracking, alkylation, isomerization, aromatization, disproportionation and the like. Often, the products from such hydrocarbon conversion processes, or portions thereof, are admixed as blending components to form motor fuels such as gasoline.
The isomerization of low molecular weight normal paraffin hydrocarbons to non-normal paraffin hydrocarbons is a well known hydrocarbon conversion process and is described in various patents, for example, U.S. Pat. Nos. 4,210,771, issued to Holcombe, and 3,150,205, issued to Krane et al. This reaction is of importance in the petroleum industry because of the higher octane number of isoparaffin hydrocarbons compared to their normal paraffin hydrocarbon counterparts. Since gasoline blends require a distribution of boiling range materials, the isoparaffins in the C.sub.4 -C.sub.7 range are valuable blending components which have a higher octane number than a corresponding gasoline fraction consisting of normal paraffins. A variety of catalysts have been prepared to catalyze the isomerization. For instance, Friedel-Crafts catalysts, such as aluminum chloride, are known to be isomerization catalysts. Halogenated catalysts, such as platinum supported on halogenated alumina support have also been used to isomerize hydrocarbons. In addition, crystalline aluminosilicate zeolites have been used in the isomerization of hydrocarbons. Both natural and synthetic crystalline aluminosilicates have been employed. Typically, the zeolites comprise a noble metal such as platinum or palladium. Included among these are the Type X and Type Y zeolites, ZSM-5 and ZSM-20 zeolites, mordenite, as well as zeolite beta.
U.S. Pat. No. 3,308,069 and Re. 28,341, both issued to Wadlinger et al., disclose a method for preparing zeolite beta. The patents disclose that zeolite beta is prepared from reaction mixtures containing tetraethylammonium hydroxide as the alkali and more specifically by heating in aqueous solution a mixture of the oxides or of materials whose chemical compositions can be completely represented as mixtures of the oxides Na.sub.2 O, Al.sub.2 O.sub.3, [(C.sub.2 H.sub.5).sub.4 N].sub.2 O, SiO.sub.2 and H.sub.2 O suitably at a temperture of about 75.degree.-200.degree. C. until crystallization occurs. The product which crystalizes from the hot reaction mixture is separated, suitably by centrifuging or filtration, washed with water and dried. The material so obtained may be calcined by heating in air or an inert atmosphere at a temperature in the approximate range of 400.degree.-1700.degree. F. or higher so long as the temperature is not sufficient to destroy the crystallinity.
U.S. Pat. No. 4,642,226, issued to Calvert et al., relates to a new and improved form of crystalline silicate having the structure of zeolite beta, to a new and useful improvement in synthesizing said crystalline silicate and to the use of said crystalline silicate as a catalyst for organic compound, e.g., hydrocarbon compound, conversion. The patent discloses the use of dibenzyldimethylammonium as a directing agent, i.e., templating agent, instead of tetraethylammonium hydroxide as described above. The patent further discloses that the zeolite beta can be ion-exchanged by conventional techniques with a salt solution. Following contact with the salt solution of the desired replacing cation, the zeolite is then preferably washed with water and dried at a temperature ranging from 65.degree. to about 315.degree. C. and thereafter may be calcined in air or other inert gas at temperatures ranging from about 200.degree. to about 600.degree. C., preferably from about 200.degree. to about 550.degree. C. for periods of time ranging from 1 to 48 hours or more to produce a catalytically active thermal decomposition product thereof. The patent discloses the use of zeolite beta in hydroisomerization of normal paraffins, when provided with a hydrogenation component, e.g., platinum.
U.S. Pat. No. 4,428,819, issued to Shu et al., discloses a process relating to the hydroisomerization of catalytically dewaxed lubricating oils using zeolite beta. The patent discloses that when the zeolites have been prepared in the presence of organic cations they are catalytically inactive, possibly because the intracrystalline free space is occupied by organic cations from the forming solution. It is further disclosed that the zeolites may be activated by heating in an inert atmosphere at 540.degree. C. for one hour, for example, followed by base exchange with ammonium salts followed by calcination at 540.degree. C. in air.
U.S. Pat. No. 4,554,145, issued to Rubin, discloses a method for the preparation of zeolite beta. In similar fashion to above cited U.S. Pat. No. 4,642,226, the patent discloses that the synthesized zeolite beta can be ion-exchanged with a salt and thereafter calcined in air or other inert gas at temperatures ranging from about 200.degree.-550.degree. C. for periods of time ranging from 1 to 48 hours or more to produce a catalytically active thermal decomposition product thereof. The patent discloses the use of zeolite beta in hydroisomerization of normal paraffins, when provided with a hydrogenation component, e.g., platinum.
U.S. Pat. No. 4,501,926, issued to LaPierre et al., discloses that petroleum distillate feedstocks may be effectively dewaxed by isomerizing the waxy paraffins without substantial cracking. The isomerization is carried out over zeolite beta as a catalyst and may be conducted either in the presence or absence of added hydrogen. The catalyst may include a hydrogenation/dehydrogenation component such as platinum or palladium in order to promote the reactions which occur. The hydrogenation/dehydrogenation component may be used in the absence of added hydrogen to promote certain hydrogenation/dehydrogenation reactions which will take place during the isomerization.
U.S. Pat. No. 4,518,485, issued to LaPierre et al., relates to a process for dewaxing a hydrocarbon feedstock with a relatively high pour point and containing paraffins selected from the group of normal paraffins and slightly branched paraffins and sulfur and nitrogen compounds which comprises subjecting said oil to hydrotreating in a hydrotreating zone operated at hydrotreating conditions sufficient to remove at least a portion of said sulfur and nitrogen compounds and subjecting said hydrotreated oil to catalytic dewaxing by contacting said oil with a catalyst comprising zeolite beta having a silica/alumina ratio of at least 30:1 and a hydrogenation component under isomerization conditions.
U.S. Pat. No. 4,554,065, issued to Albinson et al., describes a process for dewaxing a hydrocarbon feedstock with a relatively high pour point and containing paraffins selected from the group of normal paraffins and slightly branched paraffins which comprises subjecting said feedstock to catalytic dewaxing at catalytic dewaxing conditions by passing said feedstock, along with hydrogen, over a dewaxing catalyst comprising zeolite beta having a noble metal hydrogenation/ dehydrogenation component to produce a partially dewaxed product and subjecting said partially dewaxed product to catalytic dewaxing at catalytic dewaxing conditions by passing said partially dewaxed product over a catalyst comprising zeolite beta having a base metal hydrogenation/ dehydrogenation component to recover a substantially dewaxed product as a product of the process.
European Patent Application No. 0 159 846, European Patent Application No. 0 164 939 and European Patent Application No. 0 164 208 disclose particular preparation methods of zeolite beta and the use of zeolite beta in hydroisomerization of normal paraffins, when provided with a hydrogenation component, e.g., platinum.
U.S. Pat. No. 4,647,368, issued to McGuiness et al., describes an upgrading process for paraffinic naphthas which subjects a full range naphtha to hydrocracking over a zeolite beta hydrocracking catalyst to effect a selective partial hydrocracking in which the higher molecular weight n-paraffinic components of the naphtha are hydrocracked preferentially to the lower molecular weight components with concurrent isomerization of n-paraffins to isoparaffins, to form a hydrocracked effluent which comprises isobutane, C.sub.5 -C.sub.7 paraffins and relatively higher boiling naphthenes and paraffins. The hydrocracked effluent is split to remove the isobutane and the C.sub.5 and C.sub.7 paraffins with the balance of the higher boiling components being used as a reformer feed. Removal of the C.sub.5 and C.sub.7 paraffins permits improved reformer operation with the production of a higher octane product. The isomerization of the paraffins which occurs in the hydrocracking step provides a C.sub.5 -C.sub.7 paraffinic fraction which is of relatively higher octane number because of the shift to isoparaffins, permitting this component to be used as a gasoline blending component.
It can be seen from the disclosures of the above cited patents that zeolite beta has been prepared for use as a catalyst in normal paraffin isomerization processes. Accordingly, processes are sought for enhancing at least one catalytic property of zeolite beta, preferably catalytic activity and selectivity, for use in normal paraffin isomerization processes.